Managing KBC commands

The controller also accepts commands. A command write is a small protocol, not a single unconditional store. A safe path checks whether the input buffer is available, whether the command was accepted, whether a response byte should be read, and whether a retry is appropriate.

Command paths are where input libraries become brittle. The controller may be busy, the command may produce an acknowledgement, and the same output path may also carry scancode bytes. The mouse lab uses a similar command and ACK pattern, so this work prepares you for Lab 4. Keep command responses separate from normal input.

Common command bugs

Writing while the input buffer is full, ignoring timeout or error bits, retrying forever, and mixing command responses with scancodes. Keep command helpers narrow: one that writes a controller command should not also parse scancodes or update application state.